The present invention relates to solvent removal from water with hydrophobic aerogels, particularly to the preparation of hydrophobic organic aerogels, and more particular to synthetic methods for the preparation of hydrophobic organic aerogels.
The key property of the porous materials that inhibits wetting by liquid water, is hydrophobicity. This property requires that the interfacial energy of the solid-liquid, is greater than that for the solid-vapor. Such a property is inherent for many polymers; the best examples of which are polyethylene, and polytetrafluoroethylene (Teflon). Other material such as carbons and inorganic oxides, including aerogels, generally have low liquid-solid interfacial energies and their surfaces have to be chemically modified to make them hydrophobic.
Aerogels are a special class of open-cell foams derived from highly crosslinked inorganic or organic gels that are dried using special techniques to preserve the tenuous solid network. These materials have ultrafine cell/pore sizes, continuous porosity, high surface area, and a microstructure composed of interconnected colloidal-like particles or polymeric chains with characteristic diameters of 100 xc3x85. This microstructure is responsible for the unusual optical, acoustical, thermal, and mechanical properties of aerogels. By definition, these materials are prepared through the sol-gel process and can be either granular or monolithic. Organic aerogels are typically prepared from the sol-gel polymerization of resorcinol and formaldehyde and are dried through supercritical extraction of the reaction solvent. Recent efforts have focused on the ability to tailor the bulk properties of organic aerogels for specific applications. One area of interest is the design of hydrophobic organic aerogels.
While there are several reported ways to make hydrophobic silica aerogels, it has been found that silica aerogels which are doped with fluorinated organic groups exhibit the highest degree of hydrophobicity. By measurement of the contact angles for a variety of hydrophobic aerogels, including tri-methyl, tri-fluoro, and methoxy terminated siloxanes, it has been determined that the 3,3,3-trifluoropropyl containing aerogels have the highest contact angles for all cases of silica aerogels. It was found that silica aerogels doped with 30% by weight of the flouro-propyl compound, gave a contact angle xe2x89xa7150xc2x0, and was transparent. Such hydrophobic inorganic or silica aerogels are described and claimed in copending U.S. applications Ser. No. 09/957,854, filed Sep. 21, 2001, entitled xe2x80x9cMethod For Removing Organic Liquids From Aqueous Solutions and Mixturesxe2x80x9d; Ser. No. 09/957,853, filed Sep. 21, 2001, entitled xe2x80x9cSuper-Hydrophobic Fluorine Containing Aerogels; and Ser. No. 09/960,593, filed Sep. 21, 2001, entitled xe2x80x9cMethod of Oil Spill Recovery Using Hydrophobic Sol-Gels and Aerogelsxe2x80x9d. Also, see L. W. Hrubesh, xe2x80x9cSolvent Removal from Water with Hydrophobic Aerogels, J. Nanocrystalline Solidsxe2x80x9d 285 (1-3), 328-32, 2001, for the verification of hydrophobic silica aerogels.
The present invention involves the use of the hydrophobic organic aerogels for removal or organics from an oil-water mixture for example, and more specifically the present invention provides synthetic methods for the preparation of hydrophobic organic aerogels. One of these methods particularly involves the sol-gel polymerization of 1,3-dimethoxybenze or 1,3,5-trimethoxybenzene with formaldehyde in non-aqueous solvents. Other of these methods involves the sol-gel polymerization of 1,3,5-trihydroxy benzene or 1,3-dihydroxy benzene and various aldehydes in non-aqueous solvents. These methods can be applied to a variety of other sol-gel precursors and solvent systems for producing hydrophobic organic aerogels.
It is an object of the present invention to provide hydrophobic organic aerogels.
A further object of the invention is to provide a method for preparation of hydrophobic organic aerogels.
Another object of the invention is to provide methods for preparation of hydrophobic organic aerogels which can be utilized for a variety of sol-gel precursors and solvent systems.
Another object of the invention is to provide methods for the preparation of hydrophobic organic aerogels that involves the sol-gel polymerization of 1,3-dimethorybenzene or 1,3,5-trimethoxybenzene with formaldehyde in non-aqueous solvents.
Another object of the invention is to provide methods for the preparation of hydropholic organic aerogels that involves the sol-gel polymerization of 1,3,5-trihydroxy benzene (phloroglucinol) or 1,3-dihydroxy benzene (resorcinol) and various aldehydes in non-aqueous solvents.
Other objects and advantages of the invention will become apparent from the following description. Basically, the invention involves hydrophobic organic aerogels and methods for the preparation thereof. These aerogels have potential utility as new sorbants for the removal of organic pollutants from water supplies or as water-proof insulation. While one the methods is described, for example, involving sol-gel polymerization of 1,3,5-trimethoxybenzene and formaldehyde in N,N-dimethylformamide, the method can be applied to a variety of other alkylated phenol derivatives and solvent systems, such as 1,3,5-trihydroxy benzene (phloroglucinol) or 1,3-dihydroxy benzene (resorcinol) and various aldehydes (ethanol, propanal, benzyaldehyde, glutaricdialdehyde, and 4,4,4-trifluorobutanal) in non-aqueous solvents. Using a procedure analogous to the preparation of resorcinol-formaldehyde (RF) aerogels, or a procedure analogous to both the one-step base and two-stepbase/acid-catalyzed polycondensation of phloroglucinal and formaldehyde. These methods generate wet flexible gels that can be dried using either supercritical solvent extraction to generate the new (hydrophobic) organic aerogels or dried to produce the xerogel. The method of this invention involves a simple and straightforward process for the generations of hydrophobic organic aerogels.